The Syrian Democratic Forces (SDF) - a coalition of Kurdish and Arab forces - began the operation in a bid to choke off Daesh’s access to an area it uses to move weapons and militants across the border, US officials speaking on condition of anonymity said on Wednesday, Reuters reported.
"It's significant in that it's their last remaining funnel" to Europe, a US military official said.
The raid in Manbij, located in Syria’s Aleppo Province, will be supported by a small number of US special operations forces on the ground, who will be acting as advisors and staying some distance back from the frontline, the official added.
He further went on to say that airstrikes by the US-led coalition will also back up the campaign.
"They'll be as close as they need to be for the (Syrian forces) to complete the operation. But they will not engage in direct combat," the official said.
Meanwhile, US officials said the assault would be mostly comprised of Syrian Arabs rather than Kurdish fighters, who will only represent about a fifth or a sixth of the overall force.
However, the so-called Syrian Observatory for Human Rights said the majority of those taking part in the raid were from the Kurdish Popular Protection Units (YPG).
A fighter from the Kurdish People's Protection Units (YPG), part of the Syrian Democratic Forces (SDF), holds her weapon in Fatisah, Raqqah Province, May 25, 2016.
‘Turkey Not Contributing to Manbij Operation’
Meanwhile, a Turkish military source said on Wednesday that Ankara could not support the offensive because of the involvement of YPG fighters and because it was beyond the range of artillery stationed in Turkey.
"Turkey has no contribution to the support that the US gives to the YPG in Syria's Manbij region. Turkey was informed by the United States about the operation, but any contribution is out of the question," the source said.
Ankara regards the YPG as a terrorist organization, saying it is linked to the Kurdistan Workers’ Party (PKK) militant group, which has been engaged in a three-decade fight for autonomy in Turkey’s Kurdish-dominated southeast.
The YPG already controls an uninterrupted 400 kilometers (250 mile) stretch of the Syrian-Turkish frontier.
Syria has been gripped by foreign-backed militancy since March 2011. Damascus regards Turkey as one of the main supporters of the militants fighting the government forces in the Arab country.
Since late September 2014, the US along with some of its allies has been conducting airstrikes purportedly against Daesh extremists inside Syria without any authorization from Damascus or the United Nations. The air raids have failed to disband the extremists.
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